Partial stroke testing (PST) is a method used in a process control system to allow testing of a selected percentage of possible failure modes of an emergency isolation valve (EIV) without completely physically closing the valve. Generally, PST is performed via a computer control system where the system communicates with an EIV to partially close the valve and then open the valve. The purpose of PST is to determine whether an EIV is operating properly to ensure safe operation of an industrial process in the event that an emergency requires closing of the EIV. PST is common in the oil, gas, petrochemical, and power industries, and numerous computer based control systems with PST capability.
Generally, computer based PST systems are operated remotely and have relatively complicated designs, including complex wiring, multiple input/output lines, voluminous documentation, full stroke/complex calibration, and numerous design components such as boosters. Furthermore, some computer based PST systems may be sensitive to air quality, and online replacement may not be an option due to requirements of full stroke for accurate positioner calibration. Moreover, some systems may have continuous air consumption and power consumption during operation and further may have additional height requirements to a valve thus requiring more space for installation.